What Is Flow Injection Analysis?
Flow Injection Analysis (FIA) is a new concept proposed by J. Ruzikka and EH Hansen of the Technical University of Denmark in 1975, that is, reproducible processing of samples or fluids in liquid flow under thermodynamic non-equilibrium conditions. Quantitative flow analysis technology for reagent zones. It is an analysis technology that has only appeared in the past 20 years. It combined with other analysis technologies has greatly promoted the development of automated analysis and instruments, and has become a new type of micro, high-speed and automated analysis technology. Flow injection analysis has developed rapidly, and it has been widely used in many analytical fields.
- Chinese name
- Flow injection analysis
- Foreign name
- Flow Injection Analysis
- Shorthand
- FIA
- Presentation time
- 1974
- Application area
- Water quality testing, soil sample analysis, etc.
- main feature
- Simple and compact structure
- Flow Injection Analysis (FIA) is a new concept proposed by J. Ruzikka and EH Hansen of the Technical University of Denmark in 1975, that is, reproducible processing of samples or fluids in liquid flow under thermodynamic non-equilibrium conditions Quantitative flow analysis technology for reagent zones. It is an analysis technology that has only appeared in the past 20 years. It combined with other analysis technologies has greatly promoted the development of automated analysis and instruments, and has become a new type of micro, high-speed and automated analysis technology. Flow injection analysis has developed rapidly, and it has been widely used in many analytical fields.
Origin of Flow Injection Analysis
- Flow Injection Analysis (abbreviated as FIA) is a new continuous flow analysis technology proposed by Danish chemists Ruzicka J and Hansen EH in 1974. In this technique, a certain volume of sample solution is injected into a flowing, non-air-spaced reagent solution (or water) carrier stream, and the injected sample solution flows into the reaction coil to form an area and interact with the carrier. The reagents in the stream are mixed and reacted, and then enter the flow detector for measurement analysis and recording. Because the sample solution is dispersed in the reagent carrier under strictly controlled conditions, as long as the sample solution injection method, the retention time, temperature, and dispersion process in the pipeline are the same, and the reaction is not required to reach equilibrium, it can be compared according Method, measuring the concentration of the substance in the sample solution from the working curve drawn by the standard solution.
Flow injection analysis applications
- There are: water quality testing, soil sample analysis, agricultural and environmental monitoring, scientific research and teaching, fermentation process monitoring, drug research, drug testing, blood analysis, food and beverage, spectrophotometric analysis, and so on.
Key Features of Flow Injection Analysis
- The structure of the required equipment is simple and compact
- In particular, the emergence of integrated or micro-piping systems has led to a major step forward in flow injection technology. Most of the pipes used are made of polyethylene, polytetrafluoroethylene and other materials, and have good corrosion resistance.
- Simple operation and easy automatic continuous analysis
- Flow injection technology pipelines analytical processes such as absorbance analysis, fluorescence analysis, atomic absorption spectrophotometry, turbidimetry, and ion-selective electrode analysis, removing a large number of tedious manual operations in the original analysis, and using batch processes The transition to continuous automatic analysis avoids human errors in operation.
- Fast analysis speed and high precision
- Since the reaction does not need to be measured after reaching equilibrium, the analysis frequency is very high, typically 60 to 120 samples / hour. When measuring S2- in wastewater, the analysis frequency is as high as 720 samples / hour. Various conditions of the injection analysis process can be strictly controlled, so the accuracy of the analysis is improved, and the relative standard deviation can generally be within 1%.
- Less reagents and samples, wide applicability
- The amount of flow injection analysis samples and reagents required only tens of microliters to hundreds of microliters at a time,
- Not only save reagents, reduce costs, the analysis of rare samples such as blood, body fluids and other shows unique advantages. FIA can be used for a variety of analytical chemical reactions, as well as a variety of detection methods. It can also complete complex extraction, separation, and enrichment processes, so it has expanded its application range and can be widely used in clinical chemistry, medicinal chemistry, and agricultural chemistry , Food analysis, metallurgical analysis and environmental analysis.
FIA Flow injection analysis FIA instrument
Composition of flow injection analysis instrument
- A typical FIA instrument is composed of the following parts:
- Pump: Used to drive the current through a thin tube.
- Sampling valve: Reproducibly inject a certain volume of sample solution into the carrier current.
- Reactor:
- There are three types of reactors used for flow injection analysis:
- Empty tube reactor
- This kind of reactor can be divided into two kinds of straight tube and coil. Straight tube type has an inner diameter of 0.3 to 0.5mm and is often made of polyethylene, polypropylene or polyvinyl chloride. The flow of carrier current in the tube is laminar, and the broadening of the "sample plug" during migration is the combined result of longitudinal and radial diffusion. Coil type is also called spiral type. When the carrier current flows in the spiral pipe at a higher speed, the longitudinal diffusion of the "sample plug" is reduced due to the effect of centrifugal force, and the degree of broadening is reduced, thereby increasing the sampling frequency. The degree of widening decreases, and the detection sensitivity naturally increases. When the ratio of the diameter of the coil to the inner diameter of the coil is 10, the "sample plug" is three times smaller than the straight tube. Coil material can be polytetrafluoroethylene, polyethylene or polypropylene, with an inner diameter of about 0.5mm. If the inner diameter is too large, the width will be increased; if the inner diameter is too small, it will be easily blocked.
- Packed bed reactor
- This reactor is similar to a packed column in chromatography. Tubes are filled with inert particulate fillers, such as glass beads. Generally speaking, the smaller the filler diameter, the smaller the "sample plug" widens. The advantages of using a packed bed reactor are that sufficient contact in the reactor, prolonged reaction time, and high sensitivity are easily obtained, but the resistance of the carrier current to pass is large, and a high-pressure pump is required.
- Single Bead String Reactor
- In the tube, the filler with a large particle diameter of about 60 to 80% of the diameter of the tube is filled, so it is easy to obtain a regular filling structure. This reactor is 10 times smaller than the empty tube and has a higher injection frequency. The inside diameter of the reactor is about 0.5 mm. The single-bead string reactor has large current-carrying flow resistance, and ordinary peristaltic pumps can still be used as the current-carrying force.
- Detector:
- The detection methods commonly used in flow injection analysis include absorbance, turbidimetry, chemiluminescence, fluorescence, atomic absorption spectrometry, flame photometry, ion-selective electrode potential method, and voltammetry. The detectors used in the detection methods are basically divided into two categories: optical detectors and electrochemical detectors.
- Among the optical detectors, the most widely used are spectrophotometers with flow cells. A common flow cell is shown in Figure 17.37. On the premise of ensuring the transmission area of a certain optical path length (typically 10-20min), its volume should be as small as possible to reduce the ampacity and sample volume, and maintain Original diffusion mode at the reagent-sample interface to improve analysis accuracy. This requires the photoelectric detection system to be sensitive and stable. In addition, the design of the flow cell should be free of dead corners and slightly inclined to facilitate the discharge of accidental air bubbles.
- Among electrochemical detectors, flow-through ion-selective electrode detectors (see Figure 17.38) are more commonly used. Ion-selective electrode detectors use "ladder flow" potential flow cells. This flow cell has a certain angle of inclination, so that the direction of current carrying flow relative to the surface of the sensitive membrane is at the optimal position. The injected sample strip is first brought into contact with the ion-selective electrode and then with the reference electrode, creating an electromotive force between them.
- The level of the effluent is kept constant through the drain. This detection method differs from the ordinary electrode method in that the flow injection analysis method does not require the electrode potential to reach a stable value before measurement. Because the test solution flowing through the electrode surface and the flow time can be accurately controlled, the results can still be completely consistent with the static measurement, and the analysis speed can be greatly improved.
- In reagent applications, the flow injection analyzer can be assembled by itself, or the flow injection analyzer manufactured by various manufacturers can be selected.
Flow injection analysis instrument application
- In view of the convenience of operation and the diversity of microchannel design, it can be expected that this flow control technology will be widely used in life science analysis and separation and enrichment of ultra-micro metals in complex matrix samples. In the field of ultra-micro separation, the main application is still limited to solid-phase extraction and separation of ultra-minia packed column in the valve, and the combined detector is only ETAAS and ICPMS. In fact, the SI-LOV flow control system can be used with a variety of detectors, and is particularly suitable for combination with micro continuous injection detectors. The main separation and enrichment methods seen so far can be performed in this system for ultra-fine separation and enrichment operations, including valve-liquid extraction, valve microdialysis, precipitation / (co) precipitation, and hydride generation. In addition, SI-LOV's flow control characteristics make it very suitable for applications in life science analysis, including on-valve enzyme-linked immunoassay, non-destructive in situ analysis during life metabolism, in vivo analysis, and single-cell analysis. By integrating the detectors required for analysis on the valve, a true lab-on-valve analysis can be achieved. In the miniaturization of analytical instruments, SI-LOV will also be an important supplement to the related technology platforms of lab-on-a-chip or micro-total analysis system (TAS). The introduction and pretreatment of macroscopic samples are still the bottlenecks and weak links in the development of TAS. This is mainly due to the fact that macro processing technology (including traditional flow injection analysis systems) and TAS differ by five or six orders of magnitude in sample and reagent processing scale (the former is mostly 0.01 to 1 mL, while the latter is usually only 1 to 100 nL). Because SI-LOV can effectively perform microliter level fluid flow control, it may become an ideal means for TAS to solve the sample introduction and processing, and become an important part of it. In order to distinguish it from the core technology in TAS, the microfluidic analysis system believes that it is clearly proposed that the LOV is the core, and the development of a mesoscopic flow control analysis system at the level of 0.1 to 10 (100) L will further promote this mesoscopic analysis The development of the field has finally promoted the miniaturization of analytical systems and their applications in life sciences.
Flow injection analysis of fault source
- In the experiment, three sources of failure may be encountered, one is due to the nature of the sample material; the other is due to the poor performance of the flow injection analysis equipment; the third is due to the poor design of the chemical process.
- Before injecting the sample into the flow injection analysis system, it may be necessary to perform some pretreatment, such as dilution, neutralization, filtration, etc., even for samples with high concentration, high acidity (alkali) or high viscosity, Dilute the sample by pouring a few microliters of sample into the confluent flow path. If there are suspended solids in the beginning, filtering is of course inevitable, but precipitation may also form during the analysis. Solid particles may not only block the pipeline, but may also interfere with the sensor, especially in the optical system. Filtering or centrifugation can usually be used to ensure the cleanliness of the sample, but it is more difficult to prevent solid particles due to chemical reactions. However, precipitation can be prevented by adding appropriate surfactants and double detergents.
Flow injection analysis failure analysis
- Instrument malfunctions can be diagnosed by recorded peak shapes. This can be observed during chemical analysis or dispersion coefficient determination:
- Poor reproducibility when repeated injections: Check out the carry-out first. This can easily be done by alternately injecting high and low concentration samples. The method to eliminate carryover is to reduce the sampling frequency or increase the current-carrying pump speed. You can also take these two measures at the same time. Also check the valve for leaks. If you use an automated flow injection analysis system, you should also check whether the test solution in the test cup is sufficient.
- Record peaks are sluggish in response to returning to baseline. The dead volume in the system is too large (bad joints, the volume of the flow cell or its interface is too large), and it plays the role of one or several small "mixing chambers". These dead volumes must be reduced or eliminated.
- Baseline drift: In optical detection systems, the cause may be the deposition of certain substances on the window of the flow cell, which can usually be removed by injecting a reagent that can dissolve the deposit, or an appropriate washing solution or detergent Rinse the entire system. In the potential detection system, the drift may come from the change of the standard battery potential (which may be the result of the E0 value drift of the indicator electrode (and) the reference electrode) or the change of the junction potential.
- Bubbles. The carrier fluid has not been degassed, and the chemical reaction generates gas (such as a CO2 generation joint) or due to a sudden pressure drop in the flow cell (the inner diameter of the circulation ground joint is larger than the inner diameter of the access pipe, which is due to the Venturj effect. To eliminate this This effect can insert the connecting pipe deep into the joint, make the nozzle as close to the cell cavity as possible, and connect a section of 20cm long and 0.5mm inner diameter pipe at the exit of the flow cell, so that the waste liquid flows through this pipe to the next section for waste. Liquid pipe.
- Sudden noise on the peak: There are small bubbles flowing in the detector. The bubbles may appear due to the various reasons mentioned above, or it may be caused by the sample valve (or ring) not being fully filled (check Down the sampling valve)
- Signal noise is significant. Although the baseline is stable, the movement of the stylus is not smooth, and the recording peaks are jagged. Excessive pump pulsation may be a disadvantage of the pump structure. It may also be that the pump tube is not tight enough, or the pump tube is old and should be renewed (when not working. The pump tube should be loosened to extend its service life) if a potential flow cell is used. The noise may come from static electricity. To eliminate this noise, insert a small metal pipe at each end of the pump tube next to the roller bar, and short the two to ground.
- Shuangfeng. Caused by insufficient reagent caused by incomplete mixing of sample and reagent. Although the peak noise is observed in most cases, double peaks can also be encountered in extreme cases, increasing retention time (reducing pump speed), enhancing mixing (using sink method), or reducing sample volume. Can all eliminate this phenomenon.
- Rhenium has good reproducibility of peaks at low concentrations but deteriorates at high concentrations. This is caused by insufficient reagents when the sample concentration is high. The correct method is to increase the concentration of the reagent, or to dilute the sample with a higher concentration. Both measures can be used at the same time.
- negative peak. When the carrier solution is colored and the injected sample is colorless and the concentration is low, it can cause local dilution of the carrier solution and produce negative peaks. When the sample
- This phenomenon also occurs when the viscosity or chemical composition of the carrier current is large. The use of a solution with a similar matrix and sample composition as the carrier current can effectively eliminate this matrix effect. The sample is injected into an inert carrier stream before it is combined with the reagent.
- Finally, it should be pointed out that when using a valve controlled by a motor for automatic injection, if the injection valve can be restored from the injection position to the filling position within a selected time, it can be used to reduce the peak width and thus increase the sampling frequency. . The valve can be stopped at the injection position for a long enough time or all the samples in the quantitative well can be discharged, but it can also be left in the injection position for a short time and only a part of the sample can be discharged, but if the injection time is too short, The peak height may be reduced and the reproducibility may be deteriorated.
Flow injection analysis
Flow injection analysis
- This method is the simplest and more commonly used FIA method.
Flow injection analysis
- This method can be used when chemical changes occur after mixing more than two reagents.
- Figure 17.39 Multi-channel flow injection analysis
Flow injection analysis combined band method
- The combined belt method uses multiple injection valves to inject reagents and samples at the same time, so that the reagents and samples are propelled by the carrier current at the same speed in their respective pipelines, and combined into a combined belt suitable for wire transfer. In this method, the carrier current used is distilled water or buffer solution, which greatly saves reagents.
- Figure 17.40 17.41
Flow injection analysis
- The dual injection method uses a dual-channel synchronous injection valve to inject the sample solution into two different flow paths simultaneously.
- Figure 17.42 Schematic diagram of the double column method
Flow injection analysis
- This method gets rid of the traditional manual extraction operation, realizes the solvent extraction automation, and improves the efficacy.
- The flow injection extraction device is shown in Figure 17.43. src = & amp; quot
Flow injection analysis
- In FIA, the reaction coil should not be too long, and the reaction speed is required to be relatively fast. For the system with a slow reaction rate, there are certain limitations. The flow-stop method can be effectively applied to the slow analysis system of chemical reactions. This method is to accurately stop the pump (including the time and the length of the pump) at a suitable time when the sample dispersion zone enters the flow detector. Changes in absorbance, etc.) make the reaction gradually complete and improve the sensitivity of the measurement. It has been used to determine reaction constants, study reaction mechanisms, slow reaction analysis, and analysis of colored samples.
Flow injection analysis filled reactor
- In FIA, it is sometimes necessary to use solid reagents, such as Zn particles and Cd particles as reducing agents, insoluble enzymes, or ion exchange resins. At this time, the solid particles of the reagent must be packed into the column and connected to the reaction pipeline to form a packed reactor. At present, such reactors mainly include a packed reduction reactor, an immobilized enzyme reactor, and an ion-filled reactor. Figure 17.44 shows the FIA flow chart with a preconcentration column.
- Figure 17.44 Flow injection analysis flow with preconcentration column
Application Examples for Flow Injection Analysis
- Flow injection analysis is widely used. It is combined with many detection techniques and separation and enrichment techniques. It has been used for hundreds of organic or inorganic analysis, as well as some basic physical and chemical constants. It has been widely used in many fields such as environment, clinical, medicine, agriculture and forestry, metallurgical geology, industrial process monitoring, biochemistry, food, etc., especially in the fields of environmental science and clinical medicine. The analysis of several components is briefly listed below for reference.
Determination of available zinc in soil by flow injection analysis
- Flow injection extraction analysis can be used to determine available zinc in soil. The device is shown in Figure 17.45.
- Figure 17.45 Flow injection extraction analysis device
Determination of certain components in flow injection analysis water
- For the detection of F- ion content in rainwater, the F-selective electrode can be used as a detector for flow injection analysis. The detection limit is 15ng / mL, the standard deviation is less than 3%, and the analysis speed is 60 times per hour. PO4 3-ions in river water, sea water and well water can be analyzed by flow injection analysis with the help of phosphorus molybdenum blue spectrophotometry. The detection limit is 0.01ug / mL, and the analysis speed is 30 times per hour. For the analysis of arsenic content in water samples, As (V) can be reduced to As () with hydrazine sulfate in advance, and excess hydrazine can be removed with a small cation exchange column, and then detected by flow injection analysis-amperometric detector, detection limit 0.4ppb.
Determination of certain components in serum by flow injection analysis
- In order to determine the Ca2 + ion content and pH value in serum, a serum sample can be injected into the carrier current. The "sample plug" first passes through the capillary glass electrode to determine the pH value, and then flows through the Ca2 + selection electrode to measure the pCa value. With the help of an immobilized glucose oxidase column and amperometric method, the glucose content in serum can be measured indirectly. The following reactions occur when glucose passes through the enzyme column:
- Glucose + O2 + H2O glucose oxidase H2O2 + CO2
- The generated H2O2 can be detected by amperometric method using a Pt electrode, or a three-line flow injection analysis method. The reagents for each line are urease, hypochlorous acid, and phenol solutions. Urea is firstly degraded by enzymes to form NH3, and then oxidized by hypochlorous acid to chloramine, and then reacts with phenol to form indophenol blue. Spectrophotometric determination is performed at 620nm, and the detection limit is 2mmol / L. You can also use a capillary glass electrode for potentiometry to indirectly quantify the urea content from a change in pH:
- NH2CONH2 + H2O urease 2NH3 + CO2
- Combining flow injection analysis with atomic absorption spectrometry to determine lithium content in the serum of patients receiving lithium therapy. Flow injection analysis can also be used in conjunction with inductively coupled plasma emission spectroscopy.
- Combination of FIA fluorescence and kinetic analysis
- Combining the flow injection analysis method with the fluorescence spectrophotometry method greatly improves the analysis sensitivity. The ternary complex is formed by the reaction of thorium with EDTA and sulfosalicylic acid, and the thorium content in the ore can be determined by fluorescence method. The excitation wavelength was 320 nm, and the measurement wavelength was 545 nm. For radon at 80pg, the relative standard deviation of the measurement is 4%, and various metal ions are not disturbed.
- The biggest advantage of the catalytic analysis method is that the sensitivity is much higher than the general chemical analysis method, and its detection limit can reach about 10 ^ -9 mol / L. Trace I-ions can be determined based on the following catalytic reactions:
- Catalytic reaction formula can infer trace I-ions